The cost of operating airborne radar equipment in its normal operating environment dictates that training in the operation of such equipment be carried on in large measure by means of simulation. In a simulation system the display viewed by the user of the equipment responds to signals that are originally provided from external storage. For example, the display may simulate the echoes reflected when a particular azimuth angle, e.g. 360 degrees, is periodically scanned by the radar beam. In such a system the externally stored signals from which the display is generated may simulate the intensities of the echoes reflected by the actual terrain when scanned by the beam.
Early simulation equipment for this purpose relied on analog techniques to produce the image on the display screen. Such images often lacked proper focus and thus they were unclear and objectionable as far as the user was concerned. The advantages of using digital techniques which provide a clearer image on the dispaly have long been recognized. However, a relatively large amount of digital circuitry is required to implement these techniques if a direct approach is taken. In particular, where approximations are made in the prior art to limit the quantity of the required equipment and hence its cost and complexity, the resultant image is often found to lack sufficient dynamic range to provide the requisite realism of the target or terrain simulated on the screen.